National Cancer Institute

at the National Institutes of Health

Breast Cancer Prevention (PDQ®)

Patient Version

Table of Contents

What is prevention?

Cancerprevention is action taken to lower the chance of getting cancer. By preventing cancer, the number of new cases of cancer in a group or population is lowered. Hopefully, this will lower the number of deaths caused by cancer.

To prevent new cancers from starting, scientists look at risk factors and protective factors. Anything that increases your chance of developing cancer is called a cancer risk factor; anything that decreases your chance of developing cancer is called a cancer protective factor.

Some risk factors for cancer can be avoided, but many cannot. For example, both smoking and inheriting certain genes are risk factors for some types of cancer, but only smoking can be avoided. Regular exercise and a healthy diet may be protective factors for some types of cancer. Avoiding risk factors and increasing protective factors may lower your risk but it does not mean that you will not get cancer.

General Information About Breast Cancer

Key Points for This Section

Breast cancer is a disease in which malignant (cancer) cells form in the tissues of the breast.

The breast is made up of lobes and ducts. Each breast has 15 to 20 sections called lobes, which have many smaller sections called lobules. Lobules end in dozens of tiny bulbs that can make milk. The lobes, lobules, and bulbs are linked by thin tubes called ducts.

Anatomy of the female breast. The nipple and areola are shown on the outside of the breast. The lymph nodes, lobes, lobules, ducts, and other parts of the inside of the breast are also shown.

Breast cancer is the second most common type of cancer in American women.

Women in the United States get breast cancer more than any other type of cancer except skin cancer. The number of new cases of breast cancer has stayed about the same since 2003. Breast cancer is second to lung cancer as a cause of cancer death in American women. However, deaths from breast cancer have decreased a little bit every year for the past several years. Breast cancer also occurs in men, but the number of new cases is small.

White women have a slightly increased risk of breast cancer compared to other races.

Avoiding cancerrisk factors may help prevent certain cancers. Risk factors include smoking, being overweight, and not getting enough exercise. Increasing protective factors such as quitting smoking, eating a healthy diet, and exercising may also help prevent some cancers. Talk to your doctor or other health care professional about how you might lower your risk of cancer.

Dense breasts

Breast density is a factor in breast cancer risk. The level of risk depends on how dense the breast tissue is. Women with very dense breasts have a higher risk of breast cancer than women with low breast density.

Increased breast density is often an inherited trait, but it may also occur in women who have not had children, have a first pregnancy late in life, take postmenopausal hormones, or drink alcohol.

Estrogen made in the body

Estrogen is a hormone made by the body. It helps the body develop and maintain female sex characteristics. Being exposed to estrogen over a long time may increase the risk of breast cancer. Estrogen levels are highest during the years a woman is menstruating.

A woman's exposure to estrogen is increased in the following ways:

Early menstruation: Beginning to have menstrual periods at age 11 or younger increases the number of years the breast tissue is exposed to estrogen.

Late menopause : The more years a woman menstruates, the longer her breast tissue is exposed to estrogen.

Late pregnancy or never being pregnant: Because estrogen levels are lower during pregnancy, breast tissue is exposed to more estrogen in women who become pregnant for the first time after age 35 or who never become pregnant.

Combination hormone replacement therapy/Hormone therapy

Hormones, such as estrogen and progesterone, can be made into a pill form in a laboratory. Estrogen, progestin, or both may be given to replace the estrogen no longer made by the ovaries in postmenopausal women or women who have had their ovaries removed. This is called hormone replacement therapy (HRT) or hormone therapy (HT). Combination HRT/HT is estrogen combined with progestin. This type of HRT/HT increases the risk of breast cancer. Studies show that when women stop taking estrogen combined with progestin, the risk of breast cancer decreases.

Exposure to radiation

Radiation therapy to the chest for the treatment of cancer increases the risk of breast cancer, starting 10 years after treatment. The risk of breast cancer depends on the dose of radiation and the age at which it is given. The risk is highest if radiation treatment was used during puberty, when breasts are forming.

Radiation therapy to treat cancer in one breast does not appear to increase the risk of cancer in the other breast.

For women who have inherited changes in the BRCA1 and BRCA2 genes, exposure to radiation, such as that from chest x-rays, may further increase the risk of breast cancer, especially in women who were x-rayed before 20 years of age.

Obesity

Obesity increases the risk of breast cancer, especially in postmenopausal women who have not used hormone replacement therapy.

Alcohol

Drinking alcohol increases the risk of breast cancer. The level of risk rises as the amount of alcohol consumed rises.

The following are protective factors for breast cancer:

Less exposure to estrogen

Decreasing the length of time a woman's breast tissue is exposed to estrogen may help prevent breast cancer. Exposure to estrogen is reduced in the following ways:

Early pregnancy: Estrogen levels are lower during pregnancy. Women who have a full-term pregnancy before age 20 have a lower risk of breast cancer than women who have not had children or who give birth to their first child after age 35.

Breast-feeding: Estrogen levels may remain lower while a woman is breast-feeding. Women who breastfed have a lower risk of breast cancer than women who have had children but did not breastfeed.

Ovarian ablation : The ovaries make estrogen. The amount of estrogen made by the body can be greatly reduced by removing one or both ovaries. Also, drugs may be taken to lower the amount of estrogen made by the ovaries.

Late menstruation: Beginning to have menstrual periods at age 14 or older decreases the number of years the breast tissue is exposed to estrogen.

Early menopause : The fewer years a woman menstruates, the shorter the time her breast tissue is exposed to estrogen.

Exercise

Women who exercise four or more hours a week have a lower risk of breast cancer. The effect of exercise on breast cancer risk may be greatest in premenopausal women who have normal or low body weight.

Estrogen-only hormone therapy after hysterectomy

Hormone therapy with estrogen only may be given to women who have had a hysterectomy. In these women, estrogen-only therapy after menopause may decrease the risk of breast cancer. There is an increased risk of stroke and heart and blood vessel disease in postmenopausal women who take estrogen after a hysterectomy.

Treatment with tamoxifen or raloxifene lowers the risk of breast cancer in postmenopausal women. Tamoxifen also lowers the risk of breast cancer in high-risk premenopausal women. With either drug, the reduced risk lasts for several years after treatment is stopped. Lower rates of broken bones have been noted in patients taking raloxifene.

Taking tamoxifen increases the risk of hot flashes, endometrial cancer, stroke, cataracts, and blood clots (especially in the lungs and legs). The risk of having these problems increases with age. Women younger than 50 years who have a high risk of breast cancer may benefit the most from taking tamoxifen. The risk of having these problems decreases after tamoxifen is stopped. Talk with your doctor about the risks and benefits of taking this drug.

Taking raloxifene increases the risk of blood clots in the lungs and legs, but does not appear to increase the risk of endometrial cancer. In postmenopausal women with osteoporosis (decreased bone density), raloxifene lowers the risk of breast cancer for women who have a high or low risk of breast cancer. It is not known if raloxifene would have the same effect in women who do not have osteoporosis. Talk with your doctor about the risks and benefits of taking this drug.

Other SERMs are being studied in clinical trials.

Aromatase inhibitors and inactivators

Aromatase inhibitors (anastrozole, letrozole) and inactivators (exemestane) lower the risk of a new breast cancer in women who have a history of breast cancer. Aromatase inhibitors also decrease the risk of breast cancer in women with the following conditions:

Postmenopausal women with a personal history of breast cancer.

Women with no personal history of breast cancer who are 60 years and older, have a history of ductal carcinoma in situ with mastectomy, or have a high risk of breast cancer based on the Gail model tool (a tool used to estimate the risk of breast cancer).

In women with an increased risk of breast cancer, taking aromatase inhibitors decreases the amount of estrogen made by the body. Before menopause, estrogen is made by the ovaries and other tissues in a woman's body, including the brain, fat tissue, and skin. After menopause, the ovaries stop making estrogen, but the other tissues do not. Aromatase inhibitors block the action of an enzyme called aromatase, which is used to make all of the body's estrogen. Aromatase inactivators stop the enzyme from working.

Prophylactic mastectomy

Some women who have a high risk of breast cancer may choose to have a prophylactic mastectomy (the removal of both breasts when there are no signs of cancer). The risk of breast cancer is much lower in these women and most feel less anxious about their risk of breast cancer. However, it is very important to have a cancer risk assessment and counseling about the different ways to prevent breast cancer before making this decision.

Prophylactic oophorectomy

Premenopausal women who have a high risk of breast cancer due to certain changes in the BRCA1 and BRCA2 genes may choose to have a prophylactic oophorectomy (the removal of both ovaries when there are no signs of cancer). This decreases the amount of estrogen made by the body and lowers the risk of breast cancer. Prophylactic oophorectomy also lowers the risk of breast cancer in normal premenopausal women and in women with an increased risk of breast cancer due to radiation to the chest. However, it is very important to have a cancer risk assessment and counseling before making this decision. The sudden drop in estrogen levels may cause the symptoms of menopause to begin. These include hot flashes, trouble sleeping, anxiety, and depression. Long-term effects include decreased sex drive, vaginal dryness, and decreased bone density.

Cancer prevention clinical trials are used to study ways to prevent cancer.

Cancer prevention clinical trials are used to study ways to lower the risk of developing certain types of cancer. Some cancer prevention trials are conducted with healthy people who have not had cancer but who have an increased risk for cancer. Other prevention trials are conducted with people who have had cancer and are trying to prevent another cancer of the same type or to lower their chance of developing a new type of cancer. Other trials are done with healthy volunteers who are not known to have any risk factors for cancer.

The purpose of some cancer prevention clinical trials is to find out whether actions people take can prevent cancer. These may include exercising more or quitting smoking or taking certain medicines, vitamins, minerals, or food supplements.

New ways to prevent breast cancer are being studied in clinical trials.

Clinical trials are taking place in many parts of the country. Information about clinical trials can be found in the Clinical Trials section of the NCI Web site. Check NCI's list of cancer clinical trials for breast cancer prevention trials that are now accepting patients.

Changes to This Summary (10/09/2014)

The PDQcancer information summaries are reviewed regularly and updated as new information becomes available. This section describes the latest changes made to this summary as of the date above.

Editorial changes were made to this summary.

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